Recently, the production of liquid crystal display (LCD) cells with a diagonal length around 5 cm has increased as mobile phones have come into wide use and their businesses expanded. The LCD cells of this sort are provided with a thin film transistor (TFT) driving system to comply with high resolution requirement.
Each LCD cell used for mobile phones or compact information terminals is around 5 cm in diagonal length, and a lot of the cells are formed on a mother glass substrate. As such, more of these cells may be cut out of a mother glass substrate than cells that are used for ordinary personal computers. More than 90 of the 5 cm cells may be cut out of a 400 mm×500 mm mother glass substrate, as opposed to 4 cells with a diagonal length around 25 cm.
Ordinarily, thin film transistor (TFT) array and counter substrates formed on glass substrates are put together to make a mother substrate of LCD cells. Each cell of a predetermined size is then cut out from the mother glass substrate. A liquid crystal material is injected into each LCD cell, one by one, and its injection inlet is sealed. Further, polarizers are put on the outer surfaces of the glass substrates. The cell is then subjected to testing or inspection.
Testing is carried out by inspectors' visual (eye) observations. They attempt to detect defects from test image patterns on the LCD cell enabled by driving signals. In order to precisely detect multiple modes of defects, the cell is driven to display various test image patterns.
Where the number of the LCD cells cut out from the mother substrate of LCD cells increases, assembling steps of injecting liquid crystal materials into the LCD cell, putting the polarizers on the substrate, testing the LCD cells, etc. are carried out not, for each cell at a time, but for a number of the LCD cells collected together in parallel as a group.
All the LCD cells are, however, subjected to such testing steps as a group, even if one of them fails to pass previous testing steps due to defects and no further testing is necessary for it. Thus, the efficiency of testing cannot be improved.
Further, prior to the visual inspection stated above, automatic screening of the LCD cells may be done by an image data processor, or an array tester may be used to detect electrical defects of driving line configurations formed on a TFT array substrate before the TFT substrate is incorporated into the cells.
Where poor and good LCD cells, clearly judged in the automatic screening, are subjected to visual inspection together, the efficiency of such visual inspection cannot be improved either.